The processing of semiconductor wafers, substrates, photomasks, flat panel displays, compact disks and similar articles typically involves the use of highly purified processing chemicals. The high purity of the processing chemicals is necessary to prevent contamination of the product by particles which can cause defects in the finished goods. Frequently the processing chemicals are corrosive, caustic or otherwise difficult to handle.
Prior chemical delivery pumps used in low contamination systems typically have suffered from several limitations. Positive displacement pumps have often been used to allow better control over the amount of chemicals delivered. However, most positive displacement pumps provide flow rates which normally vary with time during the pumping process. Typically, positive displacement chemical delivery pumps have a pulsating outflow. Pulsating outflows develop undesired force fluctuations in associated tubing, piping, and other equipment parts and can cause fluid hammering. Hammering can be destructive to the fluid conduits and associated valving. It can also cause more general mechanical problems due to the associated vibration. Fluid hammering and vibrations also cause the generation of particles in and around the semiconductor processing machines. The generated particles cause contamination problems which are difficult to adequately rectify using filtration systems or other approaches.
Prior centrifugal and positive displacement chemical delivery pumps have also suffered problems when confronted with mixed liquid and gaseous phases in the flow stream. In some cases, such as centrifugal pumps, a mixed phase flow can cause loss of liquid in the pumping cavity. This can cause the pump to stop pumping. In positive displacement pumps the passage of mixed phase flows can result in detrimental effects on the pump and system operation. These detrimental effects are sometimes due to fluctuations in the loading experienced by the pump and associated forces, vibration and particle generation.
The current invention provides a novel bellows pump which provides an even delivery flow rate and even pressure output. It also minimizes pulsation and vibration related problems, especially particle generation. These and other benefits and advantages of the invention are set forth herein or apparent from the information given herein.